Recent studies have suggested that successful anti-tumor responses consisted of a combination of T cell-mediated and non-T cell-mediated mechanisms. We have used transplantable mouse renal and autochthonous mammary carcinoma models to demonstrate that the systemic administration of the combination of IL-2/pulse IL-12 yields enhanced antitumor effects against even well-established metastatic cancers. The systemic administration of IL-12/pulse IL-2 induces complete regression of established mouse renal cancer by a mechanism that is dependent on CD8+ T cells, the production of interferon-gamma and functional FasL. A novel latex infusion method has demonstrated a potent anti-angiogenic component to the therapy, and electron micrographic analyses have shown that apoptosis of tumor-associated endothelial cells becomes detectable within 5 days of the initiation of therapy. These results suggest that an early anti-neovascular response may be a critical early component in the process of tumor rejection. A role for Fas-mediated killing has also been demonstrated since the IL-12/pulse IL-2 combination loses most of its efficacy in mice with a dysregulated FasL(gld)gene, and Fas-overexpressing renal cancer cells grow at a reduced rate in wild- type, but not IFN-gamma -/- or gld mice. Studies are currently in progress to determine whether the Fas-mediated apoptotic effects occur at the level of the vasculature or directly on the tumor cells. Similarly, IL-12/pulse IL-2 can also induce complete regression of spontaneous mouse mammary carcinoma, and enhances expression Fas and FasL genes and the anti-angiogenic chemokines Mig and Crg-2, T cell infiltration, and apoptosis in the mammary tumor sites. Additional studies have shown that an early effect of IL-12/pulse IL-2 therapy is the induction of Mig and Crg-2 chemokine gene expression in parenchymal cells of many organs, suggesting that the rapid anti-neovascular and T cell recruiting activities of IL-12/pulse IL-2 could be initiated or enhanced by parenchymal cells. These results suggest that successful biological therapy of cancer may depend on a complex combination of immune-mediated and immune-dependent (i.e. antiangiogenic) events, and that parenchymal tissue responses may be important participants in the evolution of anti-tumore effects. These preclinical results provided the rationale for a now completed non-human primate toxicology study of the IL-12/IL-2 combination, an imminent Phase I clinical trial of this cytokine combination which will be initiated by the Division of Clinical Sciences, NCI in late 1999. - Angiogenesis, Animal models, Cancer immunotherapy, Chemokines, Cytokines, T cells, Apoptosis,